I'm having a lot of fun with your game!
The only suggestions that come to my mind right now are:
1- controls are a little ankward; space for machinegun is far from del and f5 for bombs (something like z- machinegun, x - bomb placing and z- bomb selecting would be better, for example)
2- player stats (lives, health bullets, bombs..) in the main screen would be useful
I love this game, and I think that adding some roguelike elements to it could result in something really neat and also innovative.. and there could be a great variety of new elements to create (weapons, armors, shooting enemies and so on). I've also been fascinated by a hybrid between game like this one, with great playability and simple oldstyle graphic, and a roguelike.
BTW I still like it the way it is, roguelike or not.
Thank you Robot!